Automatic travel adjuster for air brake pistons



June 1952 l. A. FARNWORTH 377 AUTOMATIC TRAVEL ADJUSTER FOR AIR BRAKEPISTONS Filed March 24, 1948 7 Sheets-Sheet 1,

Inventor Ivan A. Famwo r/h June 3, 1952 l. A. FARNWORTH 2,599,377

AUTOMATIC TRAVEL ADJUSTER FOR AIR BRAKE PISTONS Filed March 24, 1948 v 7Sheets-Sheet 2 IIDTm go Kl E 2 Inventor Ivan A. Farnwonh Attorneys June3, 1952 AUTOMATIC TRAVEL ADJUSTER FOR AIR BRAKE PISTONS Filed March 24,1948 Fig. 3.

i IE 4 l. A. FARNWORTH III VIIII' '7 Sheets-Sheet 3 Ivan A. FamworfhJune 3, 1952 l. A. FARNWORTH AUTOMATIC TRAVEL ADJUSTER FOR AIR BRAKEPISTONS Filed March 24, 1948 7 Sheets-Sheet ,4

In ventor Juan A. Farnwor/h June 3, 1952 l. A. FARNWORTH AUTOMATICTRAVEL ADJUSTER FOR AIR BRAKE PISTONS Filed March 24, 1948 7 Sheet-Sheet5 Ivan A. Farnworfh 'INVENTOR.

June 3, 19 l. A. FARNWORTH AUTOMATIC TRAVEL ADJUSTER FOR AIR BRAKEPISTONS 7 Sheets-Sheet 6 Filed March 24, "I948 [van A. Famwor/h IN V ENTOR.

BY @mwiu WW 25M June 3, 195 l. 'A. FARNWORTH AUTOMATIC TRAVEL ADJUSTERFOR "AIR BRAKE PISTONS 7 Sheet's-Sheet 7 Filed March 24, 1948 Fig. /4.

Ivan A. Farnworfh JNVENTOR.

l atentecl june 3, 1952 UNIT!) STATES PATENT OFFICE AUTOMATIC TRAVELADJUSTER FOR AIR BRAKE PISTONS 12 Claims. 1

This invention comprises novel and useful improvements in an automatictravel adjuster for air brake pistons and more specifically pertains toa mechanism for automatically maintaining an adjustment of the linkageconnecting an air brake piston with the brake mechanism for causingactuation of the brakes during a predetermined portion of the air brakepiston travel.

The principal object of this invention therefore is to automaticallyadjust the length of the connecting linkage between the air-operatedbrake-actuating piston and the brake rigging in accordance with eitherwear in the brake rigging or brake shoes, or increased thickness of newshoes when installed, so that the brake-applying stroke of the saidactuating piston will be maintained substantially continuously at agiven length.

An important object of the invention is to automatically adjust the airbrake piston travel, as set forth in the preceding object, by and duringthe brake applying movement of the brake system.

Still another object is to individually and independently adjust thebrakes of each car or other ehicle unit and thus maintain the sameeffective brake pressure and action on each in conformity with theforegoing objects.

A still further object is to provide a brake adjusting mechanismaccording to the foregoing objects for obviating the necessity formanually and laboriously adjusting the brake rigging, especially whennew brake shoes are installed or as wear occurs in said shoes or therigging.

In general, the invention is concerned with so altering the conventionalbrake-operating mechanism that slack due to wear in the brake rigging orof the brake shoes will be automatically taken up as and when it occurs,and that, upon the installation of new brake shoes the increasedthickness thereof will be automatically accommodated, to the end thatthe actuating stroke of the air-operated piston will be maintained at aconstant length.

In accordance with the presently preferred embodiment of the inventionadapted for installation in connection with existing air-brake equipmentin railroad rolling stock, the connecting rod between the air-operatedpiston and the brake rigging is made up of two independent rod memberswhich are normally joined by a ratchet coupling to form, in effect, anelongate element rigid in the direction of brake application. The pistonis fixed to an end of one of the rod members and the pawl of the ratchetcoupling to the other end. The other rod member is formed as a ratchetbar over which the pawl is arranged to operate, and is connected to thebrake rig! ging. A limit arm is fixed to the ratchet bar and extendsinto engagement with the carriage of a positioning device, beingslidable within such carriage between two abutment members, one of whichis movable to a position establishing a maximum spacing between abutmentmembers equal to the normal length of the brake-applying stroke of theratchet bar. The positioning device includes a ratchet arrangement,which permits brake-applying travel of the carriage in company with theconnecting rod members aforesaid, but prevents travel of the carriage inthe opposite direction, whereby return of the ratchet bar from. anybrake-applying position is limited, in instances where thebrake-applying stroke is normal-or too long, to the maximum spacingbetween abutment members. A resilient arrangement is provided to returnthe ratchet bar the limited extent permitted, while the usual returnspring associated with the piston serves to return the piston and itsconnecting rod member to their original positions, the pawl riding overthe ratchet bar during such return to accomplish the required elongationof the connecting rod arrangement, so that the next brake-applyingstroke of the piston will be one of normal length. A latch normallymaintains ratchet operation for the ratchet arrangement of thepositioning device, but a latch release is provided, together withactuating means therefor which is placed in proper operative position bythe return movement of the piston-carrying connecting rod member fromthose brake-applying positions involv pulsion device acts to move thecarriage in itsnormally locked direction to carry the ratchet barthrough an extended return travel, thereby shortening the connecting rodarrangement, so a that the next brake-applying stroke of the piston willbe of normal length. A clutch arrangement maintains the pawl disengagedfrom the ratchet bar so the aforesaid extended return travel of theratchet bar can be accomplished.

Accordingly, a feature of the invention resides in the provision of anextensible and retractible connecting rod arrangement between thefluidoperated piston and the brake mechanism in a fluid-operated brakesystem; and a movable positioning device embodying a travel-way ofconstant given length representing the length of a normal brake-applyingstroke, the positioning device being so constructed and arranged and soassociated with the connecting rod arrangement as to move therewith inthe brake-applying stroke, and to, in effect, both measure and apply thecorrection in length of such connecting rod arrangement necessary forproper adjustment of the system.

A further feature is the provision for normally locking the positioningdevice against movement in the direction of return of the piston andconnecting rod arrangement from brake-applying position, except when thebrake-applying stroke is excessively short as when new brake shoes havebeen applied.

These, together with various ancillary features and objects of theinvention which will be later setforth in the accompanyingspecification, are attained by the present device, a preferredembodiment. of which has been illustrated by way of example only in theaccompanying drawings, wherein:

Figure 1 is a top plan view, parts being broken away to show theinterior construction thereof, of a preferred embodiment of theinvention;

Figure 2 is a vertical transverse sectional view, upon an enlargedscale, through the adjusting arm of the device, taken substantially uponthe plane, of the section line 2-2 of Figure 1;

Figure 3 is a longitudinal vertical sectional view, taken upon anenlarged scale, parts being broken away and shown in section, throughthe reaction cylinder assembly, taken substantially upon the plane ofthe section line 3-3 of Fi ure 2;

Figure 4 is a longitudinal vertical sectional view through the adjustingrack assembly, taken substantially upon the plane of the section line4-4 of-FigureZ;

Figure 5 is a longitudinal vertical sectional View through the clutchand operating rack assembly, taken substantially upon the plane of thesection line 55 of Figure 2;

Figure 6 is a view similar to Figure 5 but showingthe parts in the brakereleasing position;

Figure 7 is a side elevational view of the cam plate-and theadjustingrack housing, taken substantially upon the plane of thesection line 'l-1of-Figure 1;

Figure'8 is a.- vertical transverse sectional view, taken upon anenlarged'scale through the clutch housing assembly, substantially uponthe plane of-the section line S8 of Figure 6;

Figure 9 is-a perspective view of an element of theadjusting rackassembly;

Figure 10 is a fragmentary top plan view, parts being broken away,showing the parts in the normal rest position of the device;

Figure 11 is a view similar to Figure 10 but showing the parts in thenormal brake operated position'of the device;

Figure 12 is a view similar-to Figure 10 but showing the parts in thenormal brake-set position, with the air brake pistonhaving too great apiston travel and the linkage being too short;

Figure 13 is a view similar to Figure 12 but showing the air brakepiston having insufiicient piston travel and the linkage being too long;

Figure. 1.4 is a perspective view, parts being broken away, of theclutch unit of; the device; and, Figure 15. is aperspective view, partsbeing;

4 broken away, of the cam plate mechanism and associated parts of theadjusting rack assembly.

Reference is now made more particularly to the accompanying drawings,wherein like numerals designate similar parts throughout the variousviews. Attention is first directed to Figure 1, wherein it designates aconventional type of air brake cylinder for operating an air brakesystem, such as employed for railway cars, it being understood that theprinciples of the invention are equally applicable to any fluid pressureoperated brake system. Slidably received in this cylinder I6, is an airpressure operated piston for operating the air brakes, indicated at l2and provided with the customary piston rod 14 which is preferably ofhollow or tubular construction as indicated at It and whichtelescopically receives a brake actuating rack or ratchet bar It towhich the piston rod is adjustably connected by a clutch unit indicatedgenerally at 20. A spring (not shown) surrounding the piston rod I2 isused to return the clutch and other parts to the original rest position.

Suitably secured in any desired manner to the outer end of the operatingrack 18, is a head 22 provided with a laterally extending integraladjustment arm 24 for a purpose to be later set forth. Likewise securedto the head 22 as by a pivot pin 25 is one end of a jack knife brakelever assembly consisting of an automatically operable lever 28 whichconsists of a member which is U-shaped in cross section, and whose outerexremity is pivoted as-at 3%) to a rod 32 connected in any suitablemanner not shown to the brake rigging with which the adjusting device isassociated. An inner brake lever 34 is secured to the lever 28 by theabove mentioned pivot pin 30, and is oscillatingly received within theU-shaped lever 28. The other end of the lever 34 is connected by a chainor cable 36 to a hand wheel or similar mechanism for operating the brakerigging alternatively to actuation of the same by the automatic brakemechanism. Pivoted to the lever 34 adjacent its mid point, as at 38, isthe bifurcated end- 40 of a brake actuating rod 42 connected to otherportions of the brake rigging with which the device is associated.

As so far described, the arrangement is such that when air or otherfluid pressure is applied to the left end of the piston 12 in thecylinder I0, the piston rod [4 and the associated operating rack I8 aremoved towards the right, thereby producing a counter-clockwise motion ofthe jack knife assembly 34' and 38'. This causes a motion towards theright of the brake rod 42 and a motion towards the left of the brake rod32, thereby operating the associated brake rigging mechanism andapplyingthe brakes. During this motion, the cable or chain 36 is slackened bymovement towards the right of the lower end of the brake lever piston.As will readily be seen, as an alternative means of operation of thebrakes, the cable or chain 36 may be tensioned 32 and 42 in the mannerabove described, but

without however causing any movement of'lever 28 and of the-associatedoperating rack l8 and piston l 2. Wherefound desirable, a spring meansindicated generally at 44 may be employed for urging the levers 28 and34" into their collapsed posltionsas shown in Figure 1*.

During this movement, it

It should be here noted that a customary con ventional air brake systemas employed on railway equipment, the brakes, rigging and levers areintended to be operated and fully applied by six inches of the pistontravel of the air brake cylinder. Further, the standard air brakecylinder piston has an over-all travel of eight-inches. It will thus beapparent that in the system here described the first one and a half ortwo-inches is used to engage and disengage the clutch, while the lastsix-inches of the eight-inch travel is employed for gradually settingthe brakes to their fully set position. With all of the brake riggingparts in proper position, it is evident that the desired relationbetween the parts may be obtained. However, as the brake shoes becomeworn, and as wear develops in the rigging, it will be evident that moreor less slack will be produced. It therefore becomes necessary toreadjust the operating linkage between the air piston and the brakerigging in order that the latter may be fully actuated within thedesired operating range of travel of the air brake cylinder piston. Thisadjustment, as formerly performed manually, was both laborious and timeconsuming. For this purpose, the present mechanism has been provided forautomatically shortening or lengthening the piston travel of the airbrake cylinder with respect to the brake operating linkage in order tofully engage the latter throughout the six-inch operating range desiredfor the air brake piston and after the initial two-inches travel fortaking up slack in the rigging. This mechanism includes the clutchindicated generally by the numeral 26, an adjusting rack assemblyindicated generally by the numeral 46, a reaction cylinder assemblyindicated by the numeral 48 and various associated mechanisms andelements to be subsequently set forth.

Clutch assembly Reference is first made to Figures 5, 6 and 14 for anunderstanding of the construction and operation of the clutch assembly.While the clutch assembly illustrated is understood to be preferable andhighly satisfactory for the present device, it will be understood thatthe principles of the invention are not limited to any particular typeof clutch, since various clutch constructions could be employed to givethe requisite clutch action. There is provided a housing 56 of anysuitable construction within which is guided for vertical slidingmovement a movable jaw 52. The movable jaw 52 is provided with atransversely extending passage therethrough and the upper surface ofthis passage is provided with a plurality of teeth 54 which when themovable jaw is lowered, are adapted to engage corresponding teeth 56upon the upper surface of the rack bar I8. As will readily be seen, theteeth 54 and 56 are positioned to engage and lock during outwardmovement of the clutch jaw, but to disengage or release during inwardmovement of the clutch jaw relative to the rack bar I8. A pair ofsprings 58.normally urge the sliding jaw 52 downwardly to lockingposition, while a cam means to be subsequently set forth raises the jawinto releasing position. It should be here noted that the housing 56 ofthe clutch assembly is rigidly carried by a connecting sleeve 66 whichsleeve is freely slidable over the operating rack 18, and is connectedin any suitable manner not shown to the end of the piston rod M forreciprocating movement therewith.

The rack bar [8 as above mentioned slides through a slot in the movablejaw 52 and also through openings in the end walls of the housing 50. Alocking dog or Slide 62 is slidably received in the lower portion of thehousing 50 beneath the movable jaw 52, and is provided with a pair oflocking lugs 64 which when disposed beneath the under surface of themovable jaw 52 urge the latter upwardly against the opposition ofsprings 58 to disengage the movable jaw teeth 54 from the rack teeth 56.However, when the slide 6'2 is properly disposed, the elevated portions64 are receivable in recesses 66 in the lower surface of the movable jaw52, thereby allowing the latter to drop downwardly under the influenceof the springs 58 to thus cause the clutch teeth 54 to engage the rackteeth 56 and thereby lock the clutch housing 50 and hence through themember 66 the piston and piston rod to the 7 operating rack [8.

The clutch dog 62 is provided with a downward- 1y extending plate 68from one side of which extends a guide 16 disposed through the wall ofthe housing 50 and slidable in a guide bushing 12 whose outer end isclosed to receive a spring 14 which urges the slide 16 inwardly of thehousing. A rod 16 is secured to the end of the slide 16, extends throughthe spring 14 and through the end wall of the cylindrical guide 12 andis provided with a collar 18 which is adapted to abut the end wall ofthe bushing 12 to prevent further inward movement of the slide under theinfluence of spring 14. This latter spring serves to yieldingly urge thedog 62 into its innermost position,

whereby the projections 64 are received in the recesses 66 thuspermitting the movable jaw 52 to drop or move downwardly and engage theclutch teeth 54 with the rack teeth 56 as above mentioned. It will thusbe seen that the spring 14 I normally actuates the dog into positionwhereby the clutch spring 58 will cause the clutch to en gage.

Means are provided for preventing the clutch engagement when the pistonof the air cylinder is in its rest position or in its first two-inchesof piston travel. There is provided a clutch dog actuating pin 86aligned with the pin 16 and extending through the other end of thehousing 50, this pin engaging one end of a spring 82 whose otherextremity seats upon the clutch dog extension plate 68. The extendingend of the pin 85 is of suflicient length to engage a suitable abutmentsurface such as that formed by the collar the spring 82 when the airbrake piston is at its rest position. The compression of spring 82 is Isufficient to over-balance the spring 14 and urge the clutch dog 62 intoits extreme right hand position as shown in Figure 6, thereby causingthe clutch to remain disengaged. As the air brake piston on itsactuating stroke moves toward the right, its first one and a half ortwo-inches of movement, of the piston merely moves the clutch housing50, while the pin 86 remains stationary, the spring 82 expanding duringthis movement. After'the requisite interim of travel have beencompleted, the tension upon the compression of spring 82 is sufiicientlyreleased to permit the spring I4 to force the dog 62 towards the left,untilthe dog projections 64 engage with a snap T action the recesses 66,as shown inFigure- 5, thereby, permitting.v the springs 58.to.engage theclutchmember. From this point, theoperating racking meansisnow rigidlylockedtothe air piston connecting rod and. moves directly therewith. Onthe returnstroke, the parts normally remain locked together until thepin 80- again engages the abutment surface 84, and onthe last two inohesof. the return stroke the dog 62. is

shiftedto the right by the increasing compression.

oispring82'thereby disengaging jaw 52. from rack I8..

Reaction cylinder assembly Attention is now directed chiefly to Figures1, 2 and-3-for an'understanding of the construction and operation of thereaction cylinder assembly.

The outermost extremity of'the adjustingarm 24' is pivotally connectedas at 86 to one end of a U- shaped'connecting rod 88' whose otherextremity has rigidly attached thereto a piston 90'slidably received ina cylinder 92 secured-in any suitable manner as by'brackets 84 to theadjusting rack assembly; The outer end of this cylinder 92 is providedwith aremovable end closure or head 96 through which slidingly extendsthe connecting rod 88' a suitable bushing 98 being provided for properlyaligning the rod 88. The other end of this cylinder is provided with aremovable closure'lflll' through Whichextends an adjusting screw I02 fora purpose to be now apparent. An

internal, rim-or flange I04 is providedadjacent' the outer end withinthe cylinder 92 to provide a stop or seat for a cup-shaped valve memberI06; which is yieldingly urged to seating-position upon the flangeIIIIIby means of a spring Hi8 adjusted by the above mentioned adjustingscrew Hi2. This valve member includes an annular periphera-1 groove III)which communicates with the interior of the valve member as by ports II2, while the peripheral groove is in register with an air pressure lineII4 extending through the side of the cylinder 92, when the-valve is inits seated position. This line I I4 is in communication with thepressure line supplying'operating pressure to the air brake actuatingcylinder It.

The arrangement of this construction is as follows: With the parts inthe rest position of the device, as shown in Figure 3, the air pressureof the brake system is supplied through pipe H4 and valve I06 to theinterior of the cylinder 92, thereby urging the piston 90and theconnecting rod 88 towards the left end of the assembly; This pressuretherefore through the adjusting arm 24 applies a constant minimum returnpressure to the operating rack I8 and the associated parts of theapparatus. On the operating stroke of the piston, the adjustingarm 24urges the reaction piston 90 inwardly of the cylinder 92, therebyfurther compressing the air within said cylinder and increasing thepressure within the reaction cylinder which urges the assembly to itsoriginal rest position. Upon the attainment of any predeterminedpressure within the reaction cylinder, the valve I06 is moved outwardlyagainst the pressure for whichv the spring I03 is adjusted, therebybreaking the connection with the pipe II4, trapping the air within thecylinder 92; and

providing a dash pot effect. Of course, upon the. return stroke of thepiston 90, thereby permitting the dropping of the pressurewithin thecylinder 92, tothe-predetermined pressure at which spring Ifllwillpermitthe valve 1 I16 tobe seated, whereby the pressure .withinthecylinder 92is again re-- stored to its original value. which is: below that of theoperating pressure: maintained in the. brake system for operating thecylinder: III: which. is equal. to the predetermined pressure at whichspring III8.is set to operate.

Adjusting rack assembly Attention is now directed to Figures '1, 2, 4and for an understanding of the construction of the adjusting rackassembly. This assembly indicated generally by the numeral 46 includes acylindrical housing IIE which is mounted in any suitable manner such asby brackets I I8 secured to the operating air cylinder I0. As shown bestin Figure 2, the cylinder III; is of square cross section and guidinglyand slidingly receives'an adjusting rackbar I therein. From inintermediate point to adjacent its outer end, the upper surface of thisrack bar.I2t| is provided with rack teeth I 22 for a purpose which willlater become apparent. At its inner end, the rack bar is provided with atransverse elongated slot I24"'which registers with a similar slot I25'formedin the side walls of the adjusting rack assembly housing IIG. arm2 extends through the slots I28 and I24 whereby movement of theadjusting arm operates the rack bar I28 as set forth hereinafter.

As shown best in Figure 4, the slotted portion I25 is provided with atransverse web or partition I28 which constitutes one abutmentof aspring I30 whose other extremity bears against the headed end I32 of arod I34 whose outer extremity slidably extends through the partition I28and is provided with a washer or collar I35 for limiting inwardmovementof the rod I34 under.

the action of spring. I30.' The arrangement is such that a slight lostmotion is provided topermit a limited movement of the adjusting. arm 24between the end or" the slot I24 and the headed end I 32.

Thus, as the operating rack I8 and the adjusting arm 24 move toward theright in Figures 1 and 4, the arm bears against the outer end or theslot I24 andbecause of the position of the teeth I22, which registerwith a latching means tobe later described, the adjustingra'ck I20 islikewise drawn to the right. However, whentheoperating rack andadjustment arm .24 start to the left as the brakes are released, underthe actionof the free action cylinder assembly previously described, acertain lost motion occurs while the arm 24 moves through the clearancein the end of the slot I24- and until. this arm contacts the headed endI312 The rack I20"is 1ocke'dor latched, further lost motion-of the arm24 is permitted by the compression of the spring I30 between thepartition I 28 and the moving head I32 on the rod I34.

A latching. means is provided for preventing rearward movement of theadjusting rack I20 under certain operating conditions of the device,andthis latching mechanism consists of a pair of lugs HIE-integrally orotherwise rising from theupper surface of the cylinder IIE, and-betweenwhichis journalled as by a pin I38, a latch I40;

" As will be clearly seen by reference-to Figures 4 and 15, one. end ofthis lever is provided with a downwardly extending jaw I42 provided withteeth I414 which are extensible through-an opening. I46 in the uppersurface of the cylinder I IB',

whereby the toothed jaw I42 may be engagedwith the teeth I22 of the rackbar Mil/thereby locking, the same against rearward movement; The otherend of the lever is providedwith a notch I48 in the upper end thereof,which notch receives abaill Hill which rests therein and loosely Anintermediate portion of the adjusting,

embraces the cylinder I I6. Cooperating complementary stop pins I52 andI54 respectively are provided on the lower and upper surfaces of thelatch member I46 and the cylinder II6 respectively, for limiting thedisengaging movement of the latch jaw I42, and also to hold spring I53used to keep the latch jaw I42 in locked position.

Secured to the side of the cylinder I I6 is a plate I56 which iscruciform in shape as shown in Figure 15. Extending laterally from theplate I56 is a cylindrical boss or bushing I58 within which isjournalled the shaft I66 having at its outer extremity an operating camI62 and rigidly at tached to its inner extremity upon a shoulderedportion I6I, see Figure 9, an actuating lever I64 provided with a notchI66 resting upon and engaging the lower end of the bail I56.

Preferably, the weight of the latch jaw I42 is such as to normally biasthe latch into its looking position with the teeth I44 engaging theteeth I 22; although as will be readily understood resilient means I53may be provided for effecting this biasing action. It will thus be seenthat the rack bar I26 may slide beneath the teeth of the latch member asthe rack bar is moved towards the right in Figure 4, but that returnmovement of the rack bar is prevented until the latch is released byoperation of the shaft I66 and the lever I64 and bail I56 by operationof the cam I62 by a mechanism to be subsequently described.

As will readily be observed by reference to Figures 2 and 15, the plateI56 has a horizontal lateral flange or rib I68 which underlies thebottom surface of the cylinder H6, while its upwardly extending rib I16abuts against and is secured to the side of the cylinder I I6. Alaterally extending rib or flange I12 is provided upon the plate I56 andconstitutes part of a cam track of a mechanism to be now described.Referring back to Figures 1, 8 and 15 and 14, it will be seen that theclutch housing 56 is provided upon one side with a pair of marginalinturned flanges I14 which comprise guide and retaining flanges for aslide I16 slidable vertically of the clutch housing. Extending laterallyfrom this slide is an operating rod I18 which extends substantially tothe vertical wall or flange I16 of the cam plate I56, and normally ridesupon the cam surface I12 thereof.

It will thus be seen that the operating rod I18 is freely slidablevertically of the clutch housing assembly within the marginal guides I14and has its end extending into close proximity to the cam plate I56,whereby the cam surfaces thereon as set forth hereinafter control thevertical position of the operating rod I18.

Referring now more specifically to Figures '1 and 14, it will be seenthat the cam plate I56 is provided with a series of cam tracks,consistin of a laterally extending cam surface I12 which at one end isprovided with a downwardly inclined ramp or run I86. Spaced from thetrack I 12 and at the same level on the plate I56 is a second tracksection I82 which likewise is provided with a downward ramp I84 adjacentthe incline I86. An intermediate track section I86 is formed on theplate I56 between the sections I12 and I82, this section having an endspaced from but overlying the incline I84 as clearly shown in Figure '1,while its other end has pivoted thereto as at I88, a movable end I96which normally bridges the gap between sections I86 and I86.

The effect of these cam track sections upon the position of theoperating rod I18 will be now described. Assuming the length of thebrake operating mechanism to be properly adjusted,

10 then with the air brake piston in its fully retracted position, andthe brakes being fully released, there is indicated at I92 in Figure '7the normal rest position of the operating rod I18, as it rests upon theupper surface of the track section I82. As now the air brake piston isoperated and applies the brakes in their fully set position, theoperating rod I 18 moves along the track section I82, down the inclineI84 beneath the end of the section I86, and then travels up the ramp I86opening the pivoted terminal I96, and emerges upon the top of the tracksection I12 coming to its rest position I94 with the brakes fully set.When the brakes are released, and the air brake piston returned to itsoriginal position, the rod I18 travels along the section I12, over thebridge section I 96, along with section I66, then upon the upper portionof the ramp I84 and so to its original position I92 upon the tracksection I82. This is the normal movement of the operating rod as thebrakes are applied and released, with the brake mechanism being inproperly adjusted position. v

The normal rest position of the parts of the assembly are shown inFigure 10, while the normal position with their brakes fully set hasbeen shown in Figure 11.

As wear occurs in the brake shoes and brake rigging, it will be evidentthat the normal piston travel of eight inches is no longer sufficient totake up the lost motion in the piston and fully set the brakes. It istherefore necessary to lengthen the brake actuating mechanism in orderto compensate for the relative shortness of the system because of theintroduction of slack therein as above mentioned.

The lengthening of the mechanism inorder to shorten the piston travel tothe desired eight inches is effected as follows: On the brake applyingstroke, after the initial two inches of movement, the clutch memberengages the operating rack and then moves the latter throughout theentire operating stroke of the air piston I2 until either limit of thisstroke has been obtained or the brakes have been fully set. During thismovement, the adjustment arm 24 hasoperated the reaction piston withinthe reaction cylinder to compress the air therein and build up apressure for returning the parts; and has simultaneously drawn theadjustment rack I26 forwardly, the rack teeth I22 slipping under the jawI42 of the dog I46, until the outermost position of the rack has beenreached. Such readjustment of the rack I26 occurs a tooth at a timesimultaneously with normal wear of the brake shoes. When now the airpressure is released upon the air piston I2, the pressure of thereaction piston 66 on the adjustment arm starts to return the parts totheir initial position. However, movement of theadjustment rack isprevented by the engagement of the dog therewith, whereby continuedreturn movement of the adjustment arm compresses the spring I36 withinthe adjustment rack, while returning the operating rack I8 and itsassociated mechanism. After about six inches of travel of the adjustmentarm and associated mechanism, the spring I36 has been fully compressed,and thereby stops further inward travel of the adjustment arm and of therack I8 At this point, the return of the air piston I2 to its originalposition under the emphasis of its own return spring, draws with it theconnecting member 66 and the clutch assembly, which latter now rachetsover the stationary operating rack I8, which movement is permitted. bymeans of theone-way engagement of :the clutch teeth and the teeth oftheoperating rack. sliding movement of the clutch continues until theclutch .assembly has approached within two inches of its rest position,whereupon the pin -80 engages the abutment 8'4 and by means of 'thecompression of the spring .82 disengages ;the clutch jaws whereupon theclutch completes its last :two inches of travel with the jaws released.Upon the next application of the brakes, the clutch housing moves twoinches before the clutch engages, whereupon the next six inches ofpiston travel, of operating rack travel, and of adjustment arm travelmerely serves to release the tension of the spring I30 by movement oftheadjustment armwithin the slot I26, without further movement of theadjustment rack. If, however, all of the slack of the piston is not yettaken up, -movement'of the air piston I2 beyond its normal eight inchesof travel will again serve to draw the adjustment rack forwardly into astill more advanced position. The return stroke of the .op-

erating rack I8 is of course limited to six inches -inthe manner setforth hereinbefore. It will thus 'be-seen that the adjustment rackserves to prevent a return stroke of the adjustment arm and theassociating operating rack of more than six inches, this sixinchesreturn stroke ibeing permitted by the compression of the spring I30.

During the above described operation for lengthening the mechanism tocompensate for wear inthe system, the control rod I18 hasmoved upon thecam track surfaces of the plate 155 in the manner previouslydescribed,the amplitude of movement barely being greater than that of the normaleight inches of travel.

When however the brake shoes of the System are replaced, it is obviousthat the increased thicknessof the newshoes as contrasted with theexcessive thinnessof theold shoes render the adjustment prevailing inthe brake mechanism. such that the brake mechanism is too long, wherebyless than eight inches of piston travel are permitted, since before theeight inches of travel had been reached the brakes by reason of theextra length of the linkage will be fully set. Obviously, in ordertoshorten the linkage and restore :the desired standard travel, it willbe necessary "to reset the adjustment rack, and for this purposethe-control rod I18 and associated mechanism is operable as follows:With thenew shoes in place, and the linkage being too long, .on thefirst application of brakes the operating rack I8, adjusting arm 24,reaction piston 90 are moved forward until the brakes are fully set,which will occur Y before the normal eight inches of travel have beeneffected. 'Thismovement is of course .Dermittedby'movement of theadjustment arm 24 in the slot 1 26 of the adjustment rack. *Dllllllgthis setting of the brakes, the adjustment rod I18 has moved from itsrest position I92, down the ramp I8l,-and upon the ramp I80. However,since the full eight inches .of travel has not been attained, theadjustment rod will not reach its normal po- .sition .194, but will stopupon the incline I80 at -aposition such as I96, which is not suflicientto clearthe pivot member 190. Therefore, on the return stroke when thebrakes are released, the adjustment rod will move from the position I96below thecam surface I86, below the incline I 84, and will pass over thecam I62 reaching a rest Position-L98 therebeyond. On the next greatoperating stroke, the control rod will move from the DOSition I98 intocontact with the c I and moon continuation of the outward traveiof thecontrol rod inQre'sponse to the setting of the brakes, will .rotate thecam and shaft I60, and operate to pulldown on the bail I50 and releasethe latch 140. Upon releasing of the latch,.which occurs obviously nearthe beginning of the brake settingstroke, the adjustment arm 24 has notyet moved sufficiently to fully release the compression of the springI30, and accordingly the latter now throws or kicks-the adjustment rackrearwardly. The completion of the brake setting stroke, will find theadjustment arm 24 at the forward end of the slot I26 in the adjustmentrack, wherebythe adjustment-rack will again be drawn to its properposition for the new adjustment arm position. Upon the return of theparts to the rest position by the release of the brakes, the adjustmentarm will travel six inches within the slot I26, com pressing the springI30 since the jaws of the dog I42 will again have engaged and locked theadjustmentrack. Thus, it will be seen that the adjustment rack "has beenreset :by the control rod and the operation of the adjustment arm to aproper position to permita six inch stroke of theoperating rack.

In drawing .the mechanism back, the clutchpin comesincontact with collar84 before the rack assembly has traveled six inches. The clutch isthereby released and the rack bar I8 is pushed back into the hollowpiston rod I4 to a new rest position.

It should be here noted that this automatic mechanism is thereforecapable of extending or shortening the operating linkage in order tomaintain a two-inch idle stroke of 'theair piston, and a six inch brakesetting strok making a total .of eight inches of piston travel.

It will be further noted that at any time the brakes may be applied bythe customary hand brake system without disturbing the setting ofdistinctly understood that the accompanying description and attacheddrawings are to be regarded as illustrative of the principles of thisinventlon, and that numerous modifications and equivalents may beresorted to falling within the scope of the appended claims.

Having described the invention, what is claimed as new is:

1. In an air brake system which includes a brake operating air piston, abrake linkage, and an operating member connected thereto, a compensatingmechanism connecting said piston and said operating member, saidcompensating'mechanism including an operating rack connected to saidoperating member, a clutch assembly engageable with said operating rackand movable with said air piston, resilient means urging said clutchintoengagement with said rack adjusting means for limiting the return strokeof the operating rack to a predetermined travel, resilient means forreturning said piston from the terminal position of its operativestroke, independent means for returning said operating memberfrom theterminal position of its operativ stroke, means preventing operation ofsaid clutch for a predetermined initial movement of said air piston, andan adjustment arm secured to said adjusting means by a lost motionconnection permitting a lost motion substantially equal to saidpredetermined travel.

2. The combination of claim 1 wherein said adjusting means furtherincludes a slide havin rack teeth thereon and an elongated slot therein,said adjustment arm engaging said slot, and a dog engaging said rackteeth.

3. The combination of claim 2 including a resilient member in said slotinterposed between said adjustment arm and said slide, and meansresponsive to predetermined variations in the length of the brakeoperating linkage for releaw ing said dog.

4. The combination of claim 3 wherein said last means includes a latchfor withdrawing said dog, a cam for operating said latch and anoperating rod carried by a part of said operating linkage forselectively operating said cam.

5. The combination of claim 4 including a guide member for saidoperating rod, said guide member having a first track for preventingengagement of said cam by said operating rod when the operating linkageis of normal length and a second track for causing engagement of saidcam by said rod when said linkage is of abnormal length.

6. The combination of claim 5 wherein said operating rod is mounted onsaid clutch assembly for vertical sliding movement thereon.

7. In a fluid-operated brake system, automatically adjustablebrake-operating mechanism including, in combination, a brake-actuatingpiston and cylinder assembly arranged for fluid operation; a connectingrod arrangement connecting the piston of said assembly with brakerigging of said system so as to apply the brakes on the power stroke ofsaid piston and release the brakes on the return stroke thereof, saidconnecting rod arrangement comprising two independent rod membersnormally joined, by a ratchet coupling, as an elongate element rigid inthe direction of brake application, one of said rod members fixedlycarrying the said piston and a pawl in spaced relationship along itslength, and the other of said rod members being connected to said brakerigging and being formed as a ratchet bar over which the said pawl isarranged to operate; a limit member fixed to the said other rod membar;a positioning device engaged by said limit member, said positioningdevice embodying a carriage having spaced abutment members between whichsaid limit member is positioned, the maximum spacing of said abutmentmembers being substantially equal to the normal length of thebrake-applying stroke of said other connecting rod member, saidpositioning device further embodying ratchet means permittingbrake-applying travel of said carriage in company with said connectingrod arrangement beyond the corresponding abutting position of said limitmember, but preventing similar movement of said carriage and said otherconnecting rod member in the opposite direction, whereby return travelof said other connecting rod member from any brakeapplying positionthereof is limited, in instances where the brake-applying stroke isnormal or too long, to the maximum spacing between said abutmentmembers; return means for said other connecting rod member; andindependently operable return means for said one connecting rod member.

8. In a fluid-operated brake system, brake-operating mechanism arrangedfor automatically taking up slack due to wear in the brake rigging orfor accommodating the installation of new brake shoes, to the end thatthe fluid-operated power stroke will be maintained at a substantiallyconstant length, said mechanism including, in combination, abrake-actuating piston and cylinder assembly arranged for fluidoperation; a connecting rod arrangement connecting the piston of saidassembly with brake rigging of said system so as to apply the brakes onthe power stroke of said piston and release the brakes on the returnstroke thereof, said connecting rod arrangement comprising twoindependent rod members normally joined, by a ratchet coupling, as anelongate element rigid in the direction of brake application, one ofsaid rod members fixedly carrying, the said piston and a pawl in spacedrelationship along its length, and the other of said rod members beingconnected to said brake rigging and being formed as a ratchet {bar overwhich the said pawl is arranged to operate; a limit member fixed to thesaid other rod member; a positioning device engaged by said limitmember, said positioning device embodying a carriage having spacedabutment members between which said limit member is positioned, themaximum spacing of said abutment members being substantially equal tothe normal length of the brake-applying stroke of said other connectingrod. member, said positioning device further embodying ratchet meanspermitting brake-applying travel of said carriage in company with saidconnecting rod arrangement beyond the corresponding abutting position ofsaid limit member, but preventing similar movement of said carriage andsaid other connecting rod member in the opposite direction, wherebyreturn travel of said other connecting rod member from any brakeapplyingposition thereof is limited, in instances where the brake-applyingstroke is normal or too long, to the maximum spacing between saidabutment members; return means for said other connecting rod member;independently operable return means for said one connecting rod member;a latch normally maintaining ratchet engagement of said ratchet means ofsaid positioning device; latch-releasing means; actuating means for saidlatch-releasing means, said actuating means being arranged for responseto movement of said one connecting rod member; guide means for saidactuating means, said guide means being arranged to place said actuatingmeans in operative position, on abnormally short brake-applying strokesof said connecting rod arrangement, for actuating said latch-releasingmeans on the next brake-applying stroke to effect ratchet disengagement;and propulsion means arranged to move said carriage in its normallylocked direction upon release of said latch.

9. In a fluid-operated brake system equipped with the following: brakemechanism, a fluid-operated piston and cylinder assembly for activatingsaid brake mechanism, and motion-transmitting linkage connecting saidpiston with said brake mechanism; an automatic piston-travel adjustermaking up part of said motion-transmitting linkage, said adjustercomprising two elongate members arranged in overlapping relationship toform a variable length connecting rod for said piston, said piston beingattached to one of said members, and said brake mechanism being attachedto the other; a clutch fixed to one of said members and arranged toengage the other of said members in various lengthwise adjustedpositions of one member relative to the other; a correction-measuringdevice embodying a travelway of given length equal to the desiredconstant length of piston travel, said travel-way being defined byspaced abutment members; a travel member fixed to saidbrake-mechanism-attached connecting rod member and arranged forreciprocative travel along said travel-way of the corrective-measuringdevice as said connecting rod member reciprocates, said device beingmovably mounted; ratchet mechanism normally preventing movement of saiddevice in the direction of return of said connecting rod and piston froma brake-applying stroke thereof while permitting movement thereof in thedirection of said brakeapplying stroke; and return means for saidconnecting rod members and piston.

10. The combination recited in claim 9, including, in addition, meansfor disengaging said ratchet mechanism; means responsive to excessivelyshort brake-applying movement of the connecting rod and piston foractuating said disengaging means; and propulsion means operativelyassociated with the correction-measuring device for moving said devicein its normally locked direction upon disengagement of said ratchetmechanism.

11. The combination recited in claim 10, wherein is provided positiveclutch-release mechanism 1.6 automatically operable at a given point onthe return stroke of the connecting rod and piston.

12. The combination recited in claim 11, wherein the clutch is a pawlfixed to the piston-attached connecting rod member, and thebrakemechanism-attached connecting rod member is a ratchet bar arrangedto be positively engaged by said pawl on the brake-appling stroke but tobe slidable relative to said pawl on the return stroke.

IVAN A. FARNWOR'IH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 556,011 Macbeth Mar. 10, 1896753,650 Wands Mar. 1, 1904 790,493 Fisher May 23, 1905 996,284 SchenckJune 27, 1911 1,749,018 Campbell Mar. 4, 1930 1,865,105 Houplain June28, 1932

